Ultrastrong and ductile steel welds achieved by fine interlocking microstructures with film-like retained austenite.

The degradation of mechanical properties caused by grain coarsening or the formation of brittle phases during welding reduces the longevity of products. Here, we report advances in the weld quality of ultra-high strength steels by utilizing Nb and Cr instead of Ni. Sole addition of Cr, as an alternative to Ni, has limitations in developing fine weld microstructure, while it is revealed that the coupling effects of Nb and Cr additions make a finer interlocking weld microstructures with a higher fraction of retained austenite due to the decrease in austenite to acicular ferrite and bainite transformation temperature and carbon activity. As a result, an alloying design with Nb and Cr creates ultrastrong and ductile steel welds with enhanced tensile properties, impact toughness, and fatigue strength, at 45% lower material costs and lower environmental impact by removing Ni.

Copper Alloy Design for Preventing Sulfur-Induced Embrittlement in Copper.

This study presents an experimental approach to address sulfur-induced embrittlement in copper alloys. Building on recent theoretical insights, we identified specific solute elements, such as silicon and silver, known for their strong binding affinity with vacancies. Through experimental validation, we demonstrated the effectiveness of Si and Ag in preventing sulfur-induced embrittlement in copper, even though they are not typical sulfide formers such as zirconium. Additionally, our findings highlight the advantages of these elements over traditional solutes, such as their high solubility and propensity to accumulate along grain boundaries. This approach may have the potential to be applied to other metals prone to sulfur-induced embrittlement, including nickel, iron, and cobalt, offering broader implications for materials engineering strategies and alloy development.

Synaptic characteristics with strong analog potentiation, depression, and short-term to long-term memory transition in a Pt/CeO2/Pt crossbar array structure.

A crossbar array of Pt/CeO2/Pt memristors exhibited the synaptic characteristics such as analog, reversible, and strong resistance change with a ratio of ∼103, corresponding to wide dynamic range of synaptic weight modulation as potentiation and depression with respect to the voltage polarity. In addition, it presented timing-dependent responses such as paired-pulse facilitation and the short-term to long-term memory transition by increasing amplitude, width, and repetition number of voltage pulse and reducing the interval time between pulses. The memory loss with a time was fitted with a stretched exponential relaxation model, revealing the relation of memory stability with the input stimuli strength. The resistance change was further enhanced but its stability got worse as increasing measurement temperature, indicating that the resistance was changed as a result of voltage- and temperature-dependent electrical charging and discharging to alter the energy barrier for charge transport. These detailed synaptic characteristics demonstrated the potential of crossbar array of Pt/CeO2/Pt memristors as artificial synapses in highly connected neuron-synapse network.

Electrical and Photocatalytic Property Change of Solution-Combusted ZnO Nanopowder by Heat-Treatment.

ZnO nanopowder was synthesized by a solution combustion method. This nanopowder was char- acterized by X-ray diffractometer (XRD), scanning electron microscope (SEM), four point probe, Hall measurement and photocatalytic reaction. The nanopowder was also investigated after heat-treating at 400 °C and 700 °C. The carrier concentrations were 8 x 10(20) cm(-3), 6 x 10(21) cm(-3) and 1.5 x 10(18) cm(-3) for the non heat-treated, the 400 °C heat-treated and the 700 °C heat-treated ZnO nanopowders respectively. Electrical resistivities of 1 Ω cm, 0.6 Ω cm and 2.6 Ω cm were obtained for the three kinds of heat-treated ZnO nanopowders respectively. These three kinds of nanopowders were then employed as photocatalysts to recover silver ions from wastewater. At 5 min of photocatalytic reaction time, the reaction removed 66.7%, 100% and 10.8% of the silver ions. The carrier concentration and photocatalytic efficiency of the 400 °C heat-treated one were 7.5 fold and 1.5 fold higher than those of the non heat-treated one respectively. However, the 700 °C heat-treated one showed far worse values than the non heat-treated one. This phenomenon was explained by carrier trap centers.

Fabrication of a TEM sample of ion-irradiated material using focused ion beam microprocessing and low-energy Ar ion milling.

Cross-section-view TEM samples of ion-irradiated material are successfully fabricated using a focused ion beam (FIB) system and low-energy Ar ion milling. Ga ion-induced damages in FIB processing are reduced remarkably by the means of low-energy Ar ion milling. There are optimized ion milling conditions for the reduction and removal of the secondary artifacts such as defects and ripples. Incident angles and accelerated voltages are especially more important factors on the preservation of a clean surface far from secondary defects and surface roughing due to Ga and Ar ion bombardment.